High pressure ethylene compression, especially at pressures of between 130 MPa and 350 MPa, is commonly employed in high pressure polyethylene production. So called “hypercompressors” are used to achieve such high pressures, the fluid ethylene becoming a “supercritical fluid” at such pressures. Poppet valves are commonly used on such hypercompressors. The hypercompressor reliability is typically the largest source of unreliability in the high pressure polymerization unit. In particular, the poppet valve life is one of the largest sources of unreliability of the hypercompressor. This unreliability is mainly due to wear of the poppet valves.
Furthermore, and perhaps leading to such high unreliability, hypercompressor valve poppets often do not open and close during operation as desired. The forces that are created by the supercritical fluid flow through the valve act upon the poppet during operation which causes the poppet to behave undesirably. The force which causes the undesirable behavior is an axial force created by a local low pressure zone between the seat and poppet sealing surfaces. Increasing the flow rate also increases the closing force on the poppet so that the poppet does not move to the open position with increasing flow rate.
What is needed is a means by which high pressure polymerization processes can be run more reliably with less down time and less expense in replacing poppet valves in the hypercompressor. The inventors have solved this and other problems in the design of a novel seat, preferably a replaceable seat, with a radial restriction between the poppet and the seat which is incorporated into a typical poppet valve design. The radial restriction is a novel concept to enable the poppet position during operation to be a function of the fluid flow conditions through the valve. This solves the problem of unwanted poppet behavior due to the forces created by fluid flow between the poppet and seat sealing surfaces. The replaceable feature enables the introduction of the seat with the novel radial restriction profile in existing valve bodies, and simplified replacement of the valve.